The present invention relates to a data reproducing technology for recorded information reproducing apparatuses such as CD-ROM (Compact Disk-Read only memory) reproducing apparatuses (CD-ROM drives).
The CD-ROM drive has rapidly become prevalent as a data reproducing apparatus for personal computers and game machines. The CD-ROM disk as an information storage medium has advantages of a large storage capacity, low cost, little degradation with elapse of time, and ease with which it can be mass-produced. Because it is based on the standard of audio CD players, however, there is a drawback that the data transfer speed and the data access speed are slow. Further, such processing as data interpolation and previous value holding is possible in audio applications when data error correction cannot be made, but such a technique makes no sense on personal computer data and it is therefore important to strengthen the data error correction capability of the data reproduction CD-ROM drive.
To cope with these problems, a variety of steps have been taken for the CD-ROM drive. They include: improving the data transfer speed by using a double speed reproduction technology, which involves raising the band of a preamplifier, strengthening the pickup servo circuit, improving the operation speed of a digital signal processing circuit and rotating the CD-ROM disk at two times the normal (standard) speed; improving the access speed (the moving speed of the pickup) by driving with a linear motor arm the pickup that reads data (signal) on the CD-ROM disk; and improving the error correction capability by using triplicated or more error correction codes instead of the existing duplicated error correction codes for the CD-ROM drive.
Further, there have recently been growing demands for high-speed access on inexpensive mechanisms that use no expensive linear motor arms, and for higher data transfer speeds. The access system currently in use employs a track count method that does not use a speed sensor. Such a technology is disclosed in Japan Patent Laid-Open Nos. 37728/1989 and 185071/1984. Generation of track crossing signals required by the track count access system is disclosed in Japan Patent Laid-Open Nos. 122939/1986 and 287924/1990. As to the data transfer speed, there are demands for improved speeds, such as four, six and eight times the normal speed (data transfer rate for the quadruple speed is some 600 Kbytes/sec).